dlink

#include<stdio.h>
#include<stdlib.h>
struct node
{
	struct node*prev;
	int info;
	struct node*next;
};
struct node*start=NULL;
struct node*tail=NULL;
void createlist(int);
void insertatbeg(int);
void insertatlast(int);
void delete();
void display();
int main()
{
	int choice,n,m,i;
	while(1)
	{
		printf("\nENTER YOUR CHOICE: \n1.CREATE LIST \n2.INSERT AT BEGINNING  \n3.INSERT AT LAST \n4.DISPLAY QUEUE \n5.DELETE QUEUE \n6.EXIT\n");
		scanf("%d",&choice);
		switch(choice)
		{
			case 1: printf("How many nodes you want?\n");
						scanf("%d",&n);
						for(i=1;i<=n;i++)
						{
							printf("Enter the element:\n");
							scanf("%d",&m);
							createlist(m);
						}
						break;
			case 2: printf("Enter the element:\n");
						scanf("%d",&m);
						insertatbeg(m);
						break;
			case 3: printf("Enter the element:\n");
							scanf("%d",&m);
							insertatlast(m);
							break;
			case 4: display();
						break;
		   case 5: delete();
		   			break;
		   case 6: exit(0);
		   default: printf("!!INVALID CHOICE!!");
		   				break;
		   }
		  }
		 return(0);
}

void createlist ( int  num)
{
	struct node*q;
	struct node*tmp;
	tmp=(struct node*)malloc(sizeof(struct node));
	tmp->info=num;
	tmp->next=NULL;
	if(start==NULL)
	{
		start=tail=tmp;
		start->prev=NULL;
	}
	else
	{
		q=start;
		while(q->next !=NULL)
		{
			q=q->next;
		}
		q->next=tmp;
		tmp->prev=q;
		tail=tmp;
		tail->next=NULL;
	}
}

void insertatbeg(int num)
{
	struct node*tmp;
	tmp=(struct node*)malloc(sizeof(struct node));
	tmp->prev=NULL;
	tmp->info=num;
	tmp->next=start;
	start->prev=tmp;
	start=tmp;
}

void insertatlast(int num)
{
	struct node*tmp;
	tmp=(struct node*)malloc(sizeof(struct node));
	tmp->info=num;
	tmp->next=NULL;
	tmp->prev=tail;
	if(start==NULL)
	{
		start=tail=tmp;
   }
  else
  {
  	tail->next=tmp;
  	tail=tmp;
  	tail->next=NULL;
  }
}

void delete()
{
	int choice, pos;
	if(start==NULL)
	{
		printf("QUEUE IS EMPTY!!");
	}
	else
	{
	struct node*tmp;
	struct node*q;
	tmp=(struct node*)malloc(sizeof(struct node));
	printf("\nEnter from which position you want to delete: \n1.DELETE FROM BEGINNING \n2.DELETE FROM LAST\n");
	scanf("%d",&choice);
	switch(choice)
	{
		case 1: tmp=start;
			start=start->next;
			if(start!=NULL)
			{
				start->prev=NULL;
			}
			printf("Deleted element is: %d\n",tmp->info);
			free(tmp);
			break;
		case 2: tmp=tail;
			tail=tail->prev;
			if(tail!=NULL)
			{
				tail->next=NULL;
			}
			printf("Deleted element is: %d\n",tmp->info);
			free(tmp);
			break;
	}
 }
}

void display()
{
	struct node*q;
	if(start==NULL)
	{
		printf("LIST IS EMPTY!!!\n");
	}
	else
	{
		q=start;
		printf("THE QUEUE IS: \n");
		while(q!=NULL)
		{
			printf("%3d",q->info);
			q=q->next;
		}
		printf("\n");
	}
}